1. Field of the Invention
The present invention relates to a programmable controller and, more particularly, to an inexpensive control circuit which may be utilized to control a physical parameter and which may be programmed for a desired value of the parameter by digital signals, which circuit requires no initial or subsequent calibration or adjustment.
2. Description of the Prior Art
In a wide variety of different types of scientific instruments, machines, and the like, there is a physical parameter which must be controlled rather accurately in order for the instrument or machine to operate as intended. One example of a common physical parameter that often must be controlled is temperature since many scientific and clinical instruments, machines, and devices must operate at a selected temperature. There is such a large number of different physical parameters that must be controlled under different circumstances that even a partial listing would be excessively long. In any event, and by way of example only, some of the more common physical parameters are light intensity, strain, position, dimensions, and the like.
When providing a control circuit for controlling a physical parameter, several requirements are usually present, but very often one or more of these requirements are not met. It is usually desirable that the control circuit be simple and inexpensive. It would be highly desirable if the circuit did not require initial or subsequent calibration or adjustment. This latter requirement is most often not fulfilled with the result being that additional circuitry is required for calibration and operator time must be taken for adjustment.
Today's instrument designs typically incorporate microprocessors and other digital circuitry. This being the case, it would be highly desirable if the control circuit were digitally programmable. This would permit the microprocessor or other digital circuitry to identify the desired value of the physical parameter and the circuit could be signaled automatically to change the actual value until the desired value is achieved. A simple, low cost, digitally programmable controller which is free from manual calibration at the time of manufacture and during the life of the controller has been unavailable heretofore.